Bigclivedotcom takes a look at how a 11kV Lightning Arrester works. When high voltage lines take a lightening hit they attempt to short it to ground to prevent passing the huge spike in voltage on down the line. The technique used is similar to what is done in a power bar on a big scale. When a high enough voltage is present in the line side a stack of MOV’s conduct the voltage to ground.
“This is a lightning arrester from an 11kV power distribution line with an interesting feature to clear itself electrically when sustained current flows through it.
Inside a robust fibreglass insulated core is a stack of MOV’s (Metal Oxide Varistors) which have a combined voltage to handle the regular peak voltage of the 11kV supply (presumably 15.5kV peak) plus a safety margin. However, when a higher voltage transient occurs on the line the MOV voltage is exceeded and they temporarily develop a lower resistance which shunts the transient to ground to protect other components on the line.
If an excessive over-voltage occurs or the MOVs start to break down after passing a modest amount of transients then there is a disconnecter attached to the bottom of the unit that will literally detonate and blow the ground cable off the end of the unit for safety. The primary function of this is to prevent the lightning arrester from passing significant current from the normal 11kV supply when it fails.”